Our hypothesis is the following: Primarily spinal syringomyelia (PSS), results from obstruction of cerebrospinal fluid (CSF) flow within the spinal subarachnoid space; this obstruction affects spinal CSF dynamics because the spinal subarachnoid space accepts the fluid that is displaced from the intracranial subarachnoid space as the brain expands during cardiac systole; in the case of primarily spinal syringomyelia (PSS), a subarachnoid block effectively shortens the spinal subarachnoid space, reducing CSF compliance and the capacity of the spinal theca to dampen the subarachnoid CSF pressure waves produced by the brain expansion during cardiac systole; the exaggerated spinal subarachnoid pressure waves occur with every heartbeat and act on the spinal cord above the block to drive CSF into the spinal cord and create a syrinx. Presyringomyelia, a recently described state of spinal cord edema associated with progressive myelopathy and obstruction in CSF flow, is a precursor stage to syringomyelia that is consistent with this hypothesis. Because of the importance of this condition to the pathophysiology of syringomyelia, we will also study patients with presyringomyelia in this protocol. After a syrinx is formed, the enlarged subarachnoid pressure waves compress the external surface of the spinal cord, propel the syrinx fluid, and promote syrinx progression.